GB2133536A

GB2133536A - Sensing alignment

Info

Publication number: GB2133536A
Application number: GB08331675A
Authority: GB
Inventors: Akiyoshi Suzuki; Hiroshi Sato; Ichiro Ishiyama
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1982-12-01
Filing date: 1983-11-28
Publication date: 1984-07-25
Also published as: DE3343206C2; FR2541471A1; GB2133536B; FR2541471B1; US4620785A; DE3348224C2; GB8331675D0; DE3343206A1

Description

1 GB 2 133 536A 1

SPECIFICATION

A sheet-like member having alignment marks and an alignment apparatus for the same BACKGROUND OF THE INVENTION

The present invention relates to a sheet-like member having alignment marks and an alignment apparatus for the same, more particularly to a reticle, mask to wafer and apparatus used therewith for manufacturing semiconductor circuits.

As a typical example of an aligner for automatically aligning plural objects, there is an aligner for manufacturing semiconductor devices, such as IC, LS1 and so on. Those [C and LSI are manufactured by superposing a number of complicated circuit patterns. The tendency toward higher processing speed and higher density of patterns, the width of the circuit lines is continuously required to be smaller and smaller, and the accuracy of alignment is required to be higher and higher even to the extent of sub-microns order. To meet such requirements, there is being developed an aligner of step-and-repeat type, which is called a stepper. In a stepper a pattern of a reticle is projected onto a wafer at a unit or reduced scale. Because of the limit to the design of the projection lens optical system, the projection area is necessarily limited or small so that the entire wafer surface cannot generally be exposed at one shot. Therefore, to cover the entire surface, the pattern is projected on a part of the water surface and stepped to the next part and projected, and this is repeated throughout an wafer. With the increase of the size of the wafer, the number of steps required for one wafer increases so that the time required for processing one wafer increases. On the other hand, prior to each of the projection of pattern, i.e., exposure of the wafer to the pattern, the reticle and the wafer must have been aligned. So, how to align them is important from the standpoint of alignment accuracy and alignment period of time. It is known, as an OFF-AXIS alignment, to first correctly place one of them at a predtermined position outside the exposure station and then move it toward the exposure position by a predetermined distance which is assured by a laser interferometer. This type enables a high speed operation, but involves problems that the alignment cannot be directly confined at the exposure station; that it cannot meet a nonlinear local distortion which may be created in the wafer with experiences of wafer process- ing; and that the accuracy of the stage movement monitoring may affect the alignment.

There is a so-called TTL type apparatus wherein the wafer is observed through the projection lens at a adjacent the exposure position to align it with the reticle. This type can meet the local distortion of the wafer and can avoid the inaccuracy in the wafer stage movement so that a better alignment between the reticle and wafer can be expected.

For the TTL system, a laser beam scanning is known for the alignment operation. An example thereof is described in a Japanese Laid-Open Patent Application No. 54-53562 which has been filed by the Assignee of the present application. Fig. 1 shows a schematical view of the device disclosed therein, for the sake of explanation. A single laser beam for a single laser beam source 1 is split or divided into two beams, which are then di- rected to the lefthand and righthand objective optical systems 11, thus allowing to detect. the displacement or degree of misalignment between the reticle 12 and wafer 13 at two positions. The two position detection allows the two kind of displacement, that is, X and Y direction (translational) displacement and 0 (rotational) displacement to be corrected, by moving one of the reticle or the wafer relative to the other.

The optical system disclosed in Fig. 1 includes a condenser lens 2 for focusing the laser beam, a polygonal mirror 3, an f-0 lens 4 and a beam splitter 5. The laser beam emitted from the laser beam generator 1 is scanningly deflected by the polygonal mirror 3 and then incident on the beam splitter 5 and et seqq. The system further includes a field lens 6, a view field splitting prism 25 which is effective also to divide the scanning laser beam into two beams. Because of the dual functions, the prism 25 may be said to be a view field dividing and spatial dividing prism. The beam is passed through or reflected by a polarization beam splitter 7, a relay lens 8 and a beam splitter 9 and reaches the objective lens 11, by which it is imaged on the objects to scan the same. The system of optical elements extending from a pupil imaging lens 14 to a detector 18 constitutes a photoelectric detection system. The device further includes a chromatic filter 15; a spatial frequency filter 16 for blocking specularly reflected (by the reticle or wafer) beams but allowing scatteredly reflected beam to transmit; an illumination optical system having a condenser lens 17, a light source 19, a condenser lens 20 and a chromatic filter 21; an observation optical system having an erector and an eye piece. The function and oper- ation of those elements are explained in detail in the above-identified Patent Application, so that detailed explanations thereof are omitted for the scale of simplicity.

In this example, the deflected beam, deflected by the polygonal mirror 3, is divided in its deflection range, by the view field dividing prism 25 which is optically conjugate with the reticle 12 and wafer 13, thus using effectively the quantity of light of the laser beam. The deflection line is traverse to the 2 GB 2 133 536A 2 edge of the prism 25. The respective beams divided out by the prism 25 are directed through the respective objective lens 11 to the alignment marks, and scan the same, respectively. The alignment scope having the microscopes has an additional important function, i.e., the observation of the alignment marks. The observation is one of the enevitable functions, particularly, in monitoring the state of alignment and initial setting of a reticle. For the observation optical system, it is desired that the images are observed in a natural and easy manner.

Fig. 2 shows the image view fields ob- served through the eye piece 23 in the arrangement of Fig. 1. In Fig. 2, reference numeral 31 depicts the view field dividing line provided by the edge of the view field splitting prism 25; 32, the scanning line of the laser beam; 33, the view field through the righthand side objective lens; and 34, the view field through the lefthand side objective. The laser beams scan the alignment mark areas in the direction connecting the righth- and and lefthand alignment marks. The alignment marks play important roles in manufacturing semi-conductor circuits, but do not provide any actual circuit patterns. So, after the wafer has been completely processed, the part thereof having the alignment marks are the non-usable areas. For this reason, the area occupied by an alignment mark is desirably as small as possible, so as to provide a better yield.

Fig. 3 shows an example of a reticle or mask (hereinafter called simply reticle). If the alignment marks are provided on the scribe lines between adjacent chips 10 1, they do not require any particular space, so that the above-described problem is solved. Since the scanning laser beam runs in the direction connecting the alignment marks, two alignment marks are arranged along this direction, that is, along and within a scribe line which is near the center of the reticle.

However, in the case of a so-called stepper type exposure and alignment device, inter alia, in the reduction stepper, it is possible that one reticle, at its entity, corresponds to one chip so that there are scribe line only at the marginal area, that is, no scribe lines near the center which would be better to accommodate the alignment marks as explained above.

Fig. 4 shows a reticle 12 having a pattern of only one chip 10 1, wherein the alignment marks are shown by reference numerals 102.

As will be understood from Fig. 4, the two alignment marks 102 are located on a line which is greatly apart from the center of the reticle 12. Therefore, at the parts of the reticle 12 which is apart from the alignment marks 102, i.e., near the bottom in Fig. 4, the alignment is not very precise, as compared with the area near the alignment mark 102, i.e., the upper side.

The deg - rading of the alignment caused by the alignment marks 102 located along a line which is far from the center of the reticle 12 is significant when the reticle 12 has a pattern of one chip. This is also problematic when the number of chips whose pattern are formed on the reticle 12 is an odd number, as compared with the case an even number of chips being formed on the reticle 12, since there is no central scribe line in the former case.

In the case where the alignment marks are provided at the opposite peripherals of the reticle pattern area at the same latitude, and the alignment marks of the wafer are located correspondingly, one of a couple of the reticle alignment marks used with a certain exposure step, i.e., a certain shot, may be overlapped with a wrong one of the wafer alignment marks for the next shot, so that correct alignment for the next shot is disabled.

When a chip pattern on a reticle is projected to a wafer, the wafer is also exposed to the reticle alignment mark patterns. If such an exposed wafer is processed, by for example, development and/or diffusion, the alignment marks on the wafer may be more or less damaged (U.S. Patent No. 3844655).-The damage may be a serious problem, when the wafer thus processed is again subjected to an additional exposure to another pattern in alignment with the existing pattern, since the wafer has to be aligned again with a reticle.

SUMMARY OF THE INVENTION

Accordingly, the principal object of the present invention is to provide a sheet-like member having alignment marks, such as a reticle or mask and wafer, by which the non-uniform alignment which may be caused by the location of the marks can be avoided so that the total alignment precision is improved.

Another object of the present invention is to provide a sheet-like member having an alignment mark, such as a reticle, mask and wafer, by which the alignment marks are so located that the undesirable overlapping of the marks can be avoided.

A further object of the present invention is to provide an alignment apparatus wherein the scanning positions are not on a line.

Another principal object of the present invention is to provide a reticle or mask by which the wafer alignment marks are not adversely affected by the exposure to the alignment marks of the reticle.

A further object of the present invention is to provide a step-and-repeat type aligner wherein the wafer alignment marks are pro- tected from adverse affect which can be caused by the exposure of the wafer to the reticle pattern more particularly, the exposure of the wafer alignment mark pattern to the reticle alignment mark pattern, Those and other objects, features and ad- hp 3 GB 2 133 536A 3 vantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiment of the present invention taken in con5 junction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows an arrangement of a prior art optical system; -Figure 2 illustrate a relationship between a scanning beam and a field of view;

Figure 3 shows an example of a mask or reticle having plural chips patterns; Figure 4 shows a prior art alignment marks for a reticle having a one-chip pattern; Figure 5 shows an arrangement of an opti cal system of an alignment apparatus accord ing to an embodiment of the present inven tion; Figure 6 shows a reticle having alignment marks according to an embodiment of the present invention; Figure 7 and Figure 8 show alignment marks on a wafer usable with the reticle of Fig. 6; Figure 9A and Figure 9B show a wafer or a reticle having alignment marks on the longitu dinal scribe line; Figure 10 shows an alignment apparatus usable with a reticle, mask or wafer having 95 the alignment marks of Fig. 9; Figure 11 illustrates a relationship between the scanning line and alignment marks of a reticle or wafer; Figure 12 shows a reticle having alignment 100 marks and light transmitting openings accord ing to an embodiment of the present inven tion; Figure 13 shows an alignment mark, on a wafer, provided on a scribe line; and Figure 14 shows a reticle having alignment marks of Fig. 8 and light transmitting openings.

DESCRIPTION. OF THE PREFERRED EMBODI- 110 MENT

Fig. 5 shows a preferred embodiment of an alignment apparatus usable with a reticle according to the present invention. The optical system shown in this Figure is similar to that of Fig. 1 optical system in some extent, so that the detailed explanation of the similar parts is omitted by assigning the same reference numerals to the element having the similar function. It is commom that the laser beam produced by the laser source 1 is scanningly deflected by a polygonal mirror 3 and are directed through the objective lenses 11 to the reticle 12 surface to scan the same with the laser beam. What is different from Fig. 1 arrangement is in the optical system after the deflected beam has been split by the view field dividing prism 25. The optical systems thereafter are not symmetrical as con- trasted to Fig. 1 arrangement. The areas scanned by the beam, which are also the areas to be observed, on the reticle or mask 12 are staggered. The areas to be observed by Fig. 5 arrangement is the areas 27 and 28 shown in Fig. 6, while the areas to be scanned by the beam are shown by the hatched areas, i.e., alignment marks X and W. Thus, the alignment marks are accommodated within the scribe street or line. This arrangement of the marks provides a long span between the couple of marks so that the rotational misalignment can be well corrected. As explained above, by changing a conventional optical system of Fig. 1, an alignment apparatus usable with the reticle 17 of the present invention can be provided.

The reticle 12 of Fig. 6 according to the present invention includes a base plate 104 on which there is pattern area 105. The pattern area has a circuit pattern to be repeatedly projected or printed onto a wafer through a projection optical system in a matrix form or in orthogonal arrays. The alignment marks X and W are so disposed that the pattern area is interposed between the alignmemt marks, which are staggeredly arranged with respect to the directions of the orthogonal arrays.

Figs. 7 and 8 show the alignment marks located on the scribe lines 107 on the wafer 13. The wafer 13 of either of those Figures is repeatedly exposed to a pattern of one-chip reticle, by step-and-repeat process. The alignment marks are accommodated within the scribe line or streets 107 which define the respective pattern areas in either cases, but the exact position of the marks are different between Fig. 7 and Fig. 8. As will be understood from Fig. 6, the alignment marks X and W for a reticle are positioned upper right and lower left as a couple. In Fig. 7, a scribe street 107 is commonly used for an alignment mark of a pattern area and an alignment mark of the adjacent pattern area. For example, around a chip 30, the four marks 30A, 3013, 30C and 30D are provided, but only the two marks 30B (X) and 30C (W) are used for the alignment of the chip 30. The mark 30A is for the upper chip 29, and the mark 301), for the lower chip 31.

In Fig. 8 arrangment, the street 107 is divided into two narrower sheets, and the alignment marks for a chip is located as near as possible to the associated chip. By using a half of the street for the alignment mark for a chip, the other half can be regarded as being remained for later use. This is advantageous. However, Fig. 7 is advantageous in that a narrower scribe street is enough. The recent trend for a narrower scribe street can be met by the Fig. 7 arrangement.

In the foregoing, the alignment marks on the wafer 13 are located along a scribe street which extends in the lateral direction in the Figures. The staggered arrangement is effec- tive in the case where the alignment marks 4 GB2133536A 4 are located along a longitudinal scribe street. Fig. 9A and 9B show an example of this. In this case, the reticle 12 has four pattern areas A, B, C and D for four chips as shown in Fig.

9B, which are projected by step-and-repeat process on the wafer 13 (Fig. 9A). The reticle 12 has a couple of alignment marks P and G in a staggered from at and outside the opposite peripheries. Those marks may be located at the positions shown by P' and Cl' as in Fig. 6 arrangement, but they may be located as shown in Fig. 913 by reference numerals P and G, which are nearer to the center of the reticle. Fig. 9A shows a part of the wafer which has been exposed to the reticle 12 of Fig. 913 by step-and-repeat exposure. It does shows the positions of alignment marks on the wafer 13. When, for example, chips 40A, 4013, 40C and 40D are exposed, the alignment marks P and G on the reticle correspond to the alignment marks 40P and 40G on the wafer. For the next shot, i.e., when chips 41 A, 41 B, 41 C and 41 D are exposed, the alignment marks P and Q on the reticle correspond to the marks 41 P and 41 CL, respectively. Since the wafer alignment marks 41 P and 41 G are not at the same latitude, there is no possibility that an alignment mark, on the wafer 13, for a certain shot is over- lapped with an alignment mark, on the reticle, for the next shot which might result in that the proper alignment cannot be achieved. In Fig. 9A, the chips having the same numeral are the ones simultaneously exposed at one shot.

Fig. 10 shows an alignment apparatus according to an embodiment of the present invention, wherein the scanning laser beams scan the alignment marks in the longitudinal direction. In order to move the laser beam longitudially, a combination of mirrors 9 and ga is used. Similarly to the optical system of Fig. 5, the lefthand and righthand optical systems are so asymmetrical that the objective lens 11 can scan the staggered alignment marks of Fig. 9, for example. In the step-andrepeat system, the pattern of the reticle 12 is projected onto the wafer 13 at each shot, and then stepped to the area of the next shot, and this is repeated. Therefore, the connection between the adjacent shots is significant. In the apparatus of Fig. 10, the wafer 13, carried on the wafer carrier 110, is stepped and positioned in X and Y directions by X- step device and Y-step device so that the chip patterns are formed in orthogonal arrays on the wafer 13. The alignmernt between the reticle 12 and the wafer 13 is achieved by a reticle holder 111 driven by X, Y and 0 drives, which means the reticle holder in X, Y and 0 directions in response to the detection of the degree of misalignment measured with the use of the alignment marks.

As described above, the marks P and Q are staggered so that it is verified that the pro- jected image P or G does not overlap the alignment mark for the next shot on the wafer 12. It is necessary that the relative positions between the marks are so predetermined that such overlapping can be avoided.

Fig. 6 and Fig. 913 show the alignment marks as being located around and adjacent to the outer peripheries of the pattern area, but the marks may be located on different inside streets at different latitudes.

As a pattern of the alignment marks, the one shown in Fig. 11 is known. The reticie 12 has the mark 51 to which the mark of the wafer 52 shown by dotted lines is aligned.

The marks are scanned by a laser beam along the line 53. The alignment apparatus of the present invention is of TTL type, so that the mark on the reticle and the mark on the wafer are simultaneously detected through the reti- cle. The detection is converted to electric signals, in response to which the mask or reticle 12 and the wafer 13 are brought into alignment. If the marks are positioned as shown in Fig. 9, and if the marks are of the same pattern, there is a possibility that the mark P position and the mark Q position are mixed to be indiscriminate when the reticle 12 and wafer 13 are rotationally deviated. This can be avoided by making the directions of the marks P and CL opposite.

Fig. 12 shows such arrangement of alignment marks. The marks P and G are oriented oppositely in their patterns. Correspondingly thereto, the alignment marks on the wafer scribe lines are formed as shown in Fig. 13. Since the orientations of the marks are opposite, they are not mixed.

According to the mark arrangements for the reticle or the like of the present invention, described in detail heretofore, the degree of alignment between the mask or reticle 12 and wafer 13 can be improved. Moreover, the undesirable overlapping of the marks can be avoided.

According to the present invention, there is also provided an alignment apparatus usable with such reticle or the like.

Another aspect of the present invention will now be described. When a chip pattern on the reticle is projected or printed onto a wafer, the alignment mark pattern of the reticle is also printed on the wafer at the wafer alignment mark position. Therefore, the area on the wafer corresponding to the reticle alignment mark is remain unexposed. The unexposed area is within the alignment mark area on the wafer. If the thus exposed wafer, as it is, is processed by for example, development, diffusion and the like, a vestige of the unexposed part is remained on the wafer alignment mark area. Such vestiges are noxious in the further alignment and exposure operation to the same wafer with another pattern which may be performed on the wafer after such processing, because they may af- P GB 2 133 536A 5 fect the alignment operation even to the extent of disabling the alignment. The present invention provides a solution to this problem. The reticle 12 shown in Fig. 12 of the present invention has windows, R and S, i.e., light transmitting portions adjacent to the alignment marks P and Q which staggeredly sandwich the pattern forming area 113.

When, for example, in Fig. 9 arrangement, the chips 40A, 4013, 40C and 40D are exposed, there remains in the mark 40Q are an unexposed part caused by the reticle alignment mark Q. The mark 40Q area on the wafer, however, is exposed to light through the window R at the next shot exposure, i.e., the shot for the chips 41 A, 41 B, 41 C and 41 D. This is repeated with the step-and-repeat exposure, so that the possibility of vestiges for the marks can be avoided.

Fig. 14 shows the windows for the same purpose but usable with the reticle 12 of Fig. 8. The windows are provided as shown by reference numerals Y and Z. The unexposed area remained, for example, in the alignment mark 109G area at the shot for the area 109, is eposed through the window Z by the shot for the area 109.

According to this aspect of the present invention, the alignment marks on the wafer for a certain pattern area, corresponding to a single or plural chips, can be sufficiently exposed to light at the shot for another pattern area, so that it is not necessary to provide a special step for the mark protection. The step- and-repeat type alignment apparatus, which is required to provide the alignment with a very severe precision, it is advantageous that the same alignment marks on the wafer can be used, since it means that the reference in- dexes are stable and unchangeable, so that a factor of causing errors can be eliminated. Also, it is advantageous that plural couple of alignment marks need not be provided.

While the invention has been described with reference.to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.

Claims

1. A sheet-like member to be aligned with another member having a pattern area, including:

a pattern area to be aligned with the pattern area of said another member; and a couple of alignment marks located outside said pattern area and so disposed that said pattern area of the sheet-like member is interposed therebetween, said alignment marks being arranged staggeredly.

2. A member according to Claim 1, wherein said alignmernt marks are located along opposite peripheries of said pattern area.

3. A member according to Claim 1, further including additional pattern areas arranged in orthogonal arrays with separation street therebetween, wherein said alignment marks for a given pattern area are disposed on different sheet.

4. A member according to Claim 2 or 3, wherein associated alignment marks have symmetric alignment mark patterns.

5. A member according to Claim 1, wherein said member is for a reticle, mask or wafer for manufacturing semiconductor circuits.

6. An alignment device for aligning two members each having at least two alignment marks by scanning the alignment marks, comprising:

means for generating scanningly deflected beams to scan the alignment marks; and optical elements disposed asymmetrically to form optical paths for introducing the beams toward the two alignment marks which are arranged staggeredly.

7. A reticle used with a step-and-repeat aligner for sequentially projecting a pattern of circuit onto a wafer in orthogonal arrays through a projection optical system, comprising:

a base plate; 1? a circuit pattern formed in a pattern area thereof; a plurality of alignment marks disposed opposing the pattern area, said alignment marks being out of any line extending along one of the orthogonal arrays.

8. A reticle used with a step-and-repeat aligner for seqentially projecting a pattern of circuit onto pattern areas of a wafer in ortho- gonal arrays through a projection optical system, comprising: a base plate; a circuit pattern formed in a pattern area thereof:

a couple of alignment marks located outside said pattern area and so disposed that said pattern area of the sheet-like member is interposed therebetween, said alignment marks being out of any line extending along any one of the orthogonal arrays; and means for exposing, when a pattern area of the wafer is exposed to the circuit pattern, an area of an alignment mark for another pattern area of the wafer to light.

9. A step-and-repeat aligner, comprising: a reticle holder for holding a reticle having a circuit pattern and an alignment mark located in a predetermined positional relationship; a projection optical system for projecting an image of the reticle; a wafer holder for holding thereon a wafer at a position where the image of the reticle is formed; stepping means for producing relative 6 GB2133536A 6 movement between said reticle holder and said wafer holder to sequentially and repeat edly exposing the wafer to the image of the reticle; means for exposing, during at least a part of time when there is no such relative move ment to allow the exposure of a part of the wafer, an area of the wafer, having an alignment mark for another part of the wafer.

10. Alignment apparatus substantially as hereinbefore described with reference to Figs.

to 14 of the accompanying drawings.

11. A mark substantially as herein de scribed with reference to Fig. 6 of the accom- panying drawings.

12. A wafer exposed by means of a mark according to claim 1.

13. An integrated circuit chip formed by exposing a semiconductor wafer to mark pat- tern on a sheet like member according to claim 1.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd-1 984. Published at The Patent Office, 25 Southampton Buildings, London, WC2A 'I AY, from which copies may be obtained.

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